US6566985B2 - High-pass filter - Google Patents

High-pass filter Download PDF

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Publication number
US6566985B2
US6566985B2 US09/956,657 US95665701A US6566985B2 US 6566985 B2 US6566985 B2 US 6566985B2 US 95665701 A US95665701 A US 95665701A US 6566985 B2 US6566985 B2 US 6566985B2
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Prior art keywords
filtering unit
casing
transmission conductor
filter
filtering
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Expired - Fee Related
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US09/956,657
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US20020036552A1 (en
Inventor
Erkki Niiranen
Tapani Vistbacka
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Powerwave Comtek Oy
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Filtronic LK Oy
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Assigned to FILTRONIC COMTEK OY reassignment FILTRONIC COMTEK OY CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: FILTRONIC LK OY
Assigned to FILTRONIC COMTEK OY reassignment FILTRONIC COMTEK OY CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: FILTRONIC LK OY
Assigned to FILTRONIC COMTEK OY reassignment FILTRONIC COMTEK OY CORRECTIVE ASSIGNMENT TO CORRECT THE PATENT NUMBER PREVIOUSLY RECORDED ON REEL 017125 FRAME 0011. ASSIGNOR(S) HEREBY CONFIRMS THE ASSIGNMENT. Assignors: FILTRONIC LK OY
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/205—Comb or interdigital filters; Cascaded coaxial cavities

Definitions

  • the invention relates to a filter realized in a conductive case by means of mechanical structural elements, which filter is suitable for signal processing especially at microwave frequencies.
  • FIG. 1 shows an example of such a prior-art filter partly opened and disassembled. It comprises resonators, such as 110 , 120 and 130 , in a row.
  • Each resonator comprises an inner conductor, such as 131 , galvanically coupled at its lower end to the bottom plate 101 of the structure.
  • the inner conductors may have extensions at their upper ends in order to increase the capacitance at the open end of the structure, thereby causing the resonator can be made shorter in the vertical dimension.
  • Each resonator further comprises an outer conductor consisting of resonator partition walls, such as 103 , and parts 102 of the side walls and end walls of the whole filter case.
  • the structure includes a conductive cover so that the filter casing is closed.
  • the cover is provided with a screw 138 at resonator 130 for tuning the resonance frequency of that resonator.
  • the capacitive coupling is between resonators 110 and 120 at their open ends where the electric field is relatively strong.
  • Conductive wings 114 , 124 attached to the inner conductors of the resonators and directed towards the aperture add to the inter-resonator coupling capacitance.
  • Input to the filter via connector IN is also capacitive.
  • the inductive coupling is between resonators 120 and 130 , near their short-circuited ends where the magnetic field is relatively strong.
  • an element 125 shaped of conductive plate, which extends close to the inner conductors of said resonators and is grounded at suitable points.
  • the element 125 produces mutual inductance between the resonators.
  • a disadvantage of the structure described and like structures is the difficulty of filter tuning and the costs that follow therefrom. Moreover, the manufacturing prior to the tuning involves relatively high costs as well. Furthermore, there is a danger of generating harmful intermodulation results, especially if the structures employ more than one metal for the purpose of temperature compensation.
  • An object of the invention is to alleviate said disadvantages associated with the prior art.
  • the structure according to the invention is characterized by that which is specified in the independent claim 1 .
  • Some preferred embodiments of the invention are specified in the other claims.
  • a metal casing houses a series of separated rigid conductive elements. Between the consecutive elements there is arranged a suitable capacitance which is adjustable within certain limits, if necessary. At least some of the conductive elements are connected with, or they include, a conductor less than half a wavelength long, short-circuited at the opposite end. Together with the casing connected to the signal ground the conductor constitutes a transmission line which, looking from the conductive element, is inductive at the operating frequencies. This way a signal path is provided in the filter, having capacitance in the longitudinal direction and inductance in the transversal direction, always between two capacitive parts.
  • the structure is a high-pass type structure.
  • An advantage of the invention is that the filter structure according to it is simple in comparison with structures according to the prior art. This means savings in manufacturing costs. Another advantage of the invention is that the structure according to it is sturdy in comparison with the prior art. This means relatively good power handling capacity and reliability. A further advantage of the invention is that the structure according to it, in comparison with the prior art, has less boundaries that may cause harmful intermodulation.
  • FIG. 1 shows an example of a filter structure according to the prior art
  • FIGS. 2 a,b show an example of a filter structure according to the invention
  • FIG. 3 shows a second example of a filter structure according to the invention
  • FIG. 4 shows a third example of a filter structure according to the invention
  • FIG. 5 shows an equivalent circuit of a structure according to the invention
  • FIG. 6 shows an example of the amplitude response of a filter according to the invention.
  • FIG. 1 was already discussed in connection with the description of the prior art.
  • FIG. 2 a shows an example of a structure according to the invention.
  • the Figure shows a conductive casing, cut open and the cover removed, in which the bottom 201 and frame 202 form a single piece.
  • the signal is brought in at the end which in the Figure is the farther end and taken out at the opposite end, which in the Figure is the nearer end.
  • In the casing there are, successively in the longitudinal direction, starting from the input end of the filter, an input conductor 2 IN, three mutually alike filtering units 210 , 220 and 230 , and an output conductor 2 OUT.
  • the first filtering unit 210 comprises a horizontal part 213 rectangular in the horizontal plane, vertical parts 211 , 212 transversal in the vertical plane, located at opposing ends in the longitudinal direction of the horizontal part, and an oblong conductive protrusion 214 transversal in the horizontal plane, extending out from the middle of a longitudinal side of the horizontal part 213 .
  • Such a piece may be produced e.g. by first cutting a suitably shaped planar piece from a rigid metal plate and then bending the protrusions corresponding to the vertical parts at a right angle.
  • the first filtering unit is supported by insulating elements, such as 250 , so that it is elevated from the bottom of the casing.
  • “Longitudinal direction” means in this description and in the claims the direction of the center line of the bottom of the filter casing from the input end of the filter towards the output end thereof.
  • “transversal direction” means the direction perpendicular to the longitudinal direction in the horizontal plane.
  • “horizontal plane” means in this description and in the claims the plane parallel to the bottom of the filter casing
  • “vertical direction” means the direction perpendicular to the bottom of the filter casing
  • “vertical plane” means the plane perpendicular to the bottom of the filter casing.
  • said conductive protrusion 214 forms a transmission line.
  • the conductive protrusion part of such transmission lines be called a transmission conductor.
  • the transmission line is short-circuited by means of a conductive piece 205 extending to the bottom 201 of the casing.
  • the length of the transmission line is chosen such that at the filter operating frequencies and stop-band frequencies half a wavelength is greater than the length of the transmission line.
  • the short-circuited transmission line is then inductive as measured at the starting end.
  • the horizontal part 213 provides in principle a short transmission line together with the bottom of the case. The distance of the horizontal part from the bottom of the case is chosen such that the “line” impedance is e.g. 50 ohm.
  • the second filtering unit 220 correspondingly comprises a horizontal part 223 , a first vertical part 221 , a second vertical part 222 , and a transversal transmission conductor 224 connected to the ground at its outer end.
  • the first vertical part 221 of the second filtering unit and the second vertical part 212 of the first filtering unit face each other and are located relatively close to one another. Thus they form an air-insulated capacitor with a certain capacitance C 12 .
  • a similar capacitive coupling exists between the second and third filtering units.
  • a similar capacitive coupling also exists between the third filtering unit and said output conductor 2 OUT as well as at the input end of the filter between said input conductor 2 IN and the first filtering unit.
  • the vertical part 221 has a relatively narrow part 221 a separated by a vertical slot, which narrow part can be bent in order to fine-tune the capacitance C 12 . If necessary, the fine-tuning of the other series capacitances can be arranged similarly.
  • FIG. 2 b shows a longitudinal section of the structure depicted in FIG. 2 a. Shown in the Figure are the bottom 201 , frame 202 and the cover 203 of the filter casing. On the signal path there are, in this order, the input conductor 2 IN, three filtering units 210 , 220 , 230 and the output conductor 2 OUT. Between these there are, respectively, the capacitances C 11 , C 12 , C 23 and C 3 o.
  • the Figure also shows a wire WI that connects the inner conductor of the coaxial input connector to the input conductor 21 N, and a wire WO which connects the output conductor 2 OUT to the inner conductor of the coaxial output connector.
  • the outer conductors of the input and output connectors are in galvanic contact with the filter casing.
  • FIG. 3 shows a second example of a structure according to the invention.
  • a filter casing cut open, with a bottom 301 and frame 302 .
  • the first filtering unit 310 comprises a horizontal part 313 rectangular in the horizontal plane, vertical parts 311 , 312 transversal in the vertical plane, located at opposing ends in the longitudinal direction of the said horizontal part, and a vertical transmission conductor 314 , in this example cylindrical, extending from the lower surface of the horizontal part 313 to the bottom of the casing.
  • the vertical conductor 314 replaces both the horizontal transversal transmission conductor 214 and the short-circuit piece 205 .
  • the vertical conductors of all the filtering units e.g. by extrusion so that they are protrusions from the bottom 301 of the casing and form a single piece with the bottom and frame.
  • the filter unit parts which have a longitudinal section resembling a broad U, are attached e.g. by soldering or with screws.
  • the vertical conductors may be so strong that special supportive elements are not needed for the filtering units.
  • FIG. 4 shows a third example of a structure according to the invention. This is similar to the structure of FIG. 2 with the following differences:
  • the transversal transmission conductor 424 of the second filtering unit 420 turns upwards providing a short-circuit to the cover 403 of the filter casing instead of the bottom. Attachment to the cover of the casing is realized by means of a screw 425 .
  • the upward-pointing part forms in this example a single piece with the second filtering unit 420 .
  • the transmission conductor of the third filtering unit 430 extends to the cover of the filter case. Instead the transmission conductor 414 of the first filtering unit goes straight to the side wall of the case.
  • the structure of FIG. 4 additionally comprises a conductive partition wall 470 .
  • the aim of the partition wall 470 is to weaken undesired electromagnetic coupling between the filtering units.
  • the capacitors in the structures are air-insulated.
  • the insulator may naturally be some dielectric material, in which case the desired capacitance values can be realized with capacitors of smaller size.
  • the insulator blocks may be produced e.g. by means of injection moulding, using plastics of suitable permittivity. Such insulator blocks may be shaped so that there is no need for special dielectric support elements for filter units, such as element 250 in FIG. 2 a.
  • FIG. 5 shows a simplified equivalent circuit corresponding to the structures of FIGS. 2, 3 and 4 discussed above.
  • the second poles of the filter input port IN and output port OUT are connected to the signal ground.
  • capacitors Ci 1 , C 12 , C 23 and C 3 o are, connected in series, capacitors Ci 1 , C 12 , C 23 and C 3 o, in that order.
  • Ci 1 corresponds to the capacitance between the input conductor, such as 2 IN
  • the first filtering unit corresponds to the capacitance between the first and second filtering units
  • C 23 to the capacitance between the second and third filtering units
  • C 3 o corresponds to the capacitance between the third filtering unit and the output conductor, such as 2 OUT.
  • the equivalent circuit further comprises three coils, each with one end in the signal ground: Coil L 1 is connected to the signal ground between capacitors CiI and C 12 , coil L 1 between capacitors C 12 and C 23 , and coil L 3 between capacitors C 23 and C 3 o. Coil L 1 corresponds to the inductance constituted by the transmission line associated with the first filtering unit, coil L 2 to the inductance constituted by the transmission line associated with the second filtering unit, and coil L 3 corresponds to the inductance constituted by the transmission line associated with the third filtering unit.
  • the inductance values depend on the frequency, being based on a short-circuited transmission line.
  • the ladder structure according to FIG. 5 with series capacitance and cross inductance is, as known, by nature a high-pass type structure.
  • FIG. 6 shows an example of the amplitude response of a filter according to the invention.
  • the vertical axis represents parameter S 21 which characterizes signal attenuation in the filter.
  • the variable on the horizontal axis is frequency.
  • Curve 61 shows that attenuation over the frequency range 1.7 to 2.0 GHz is very low.
  • Attenuation increases rapidly from 1.6 GHz down. For example, at 900 MHz the attenuation already is about 65 dB. Above 2 GHz the attenuation increases a little; e.g. at 2.5 GHz it is about 4 dB.
  • a filter with this kind of response is suitable as an antenna filter part that passes e.g. the signals of the GSM1800 system but stops GSM900 signals when using a dual-band antenna.
  • the result presented in FIG. 6 applies to a structure comprising three filtering units in accordance with the examples discussed above.
  • the steep slope of the attenuation curve 61 below the pass band is reached when the structure is made to function according to Chebyshev approximation in the frequency band in question.
  • the invention is not limited solely to those.
  • the elements constituting the filtering units may be shaped in many ways: They may be e.g. rectangular prisms from which the transmission conductor starts or they may have curved edges. Their quantity is naturally freely selectable. Nor does the invention limit the manufacturing method of the structure. The inventional idea may be applied in different ways within the scope defined by the independent claim.
US09/956,657 2000-09-22 2001-09-19 High-pass filter Expired - Fee Related US6566985B2 (en)

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FI20002090A FI115331B (fi) 2000-09-22 2000-09-22 Ylipäästösuodatin
FI20002090 2000-09-22

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090153270A1 (en) * 2007-12-11 2009-06-18 Telegaertner Karl Gaertner Gmbh High-pass filter
CN102265456B (zh) * 2008-12-25 2014-12-24 日本电气株式会社 基于组合导通孔结构的滤波器
CN106463805A (zh) * 2014-03-24 2017-02-22 瑞典爱立信有限公司 同轴滤波器及其制造方法

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060263550A1 (en) * 2004-12-10 2006-11-23 Charles Nichols Print receptive topcoat for ink jet printing media
DE102016117415B4 (de) 2016-09-15 2019-10-31 Kathrein Mobilcom Austria Gmbh Hochfrequenzfilter mit verbesserter Signaleinkopplung bzw. Signalauskopplung

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4179673A (en) 1977-02-14 1979-12-18 Murata Manufacturing Co., Ltd. Interdigital filter
US5124675A (en) * 1989-02-16 1992-06-23 Electric Industry Co., Ltd. LC-type dielectric filter
US5307036A (en) * 1989-06-09 1994-04-26 Lk-Products Oy Ceramic band-stop filter
US5379011A (en) * 1992-10-23 1995-01-03 Motorola, Inc. Surface mount ceramic filter duplexer having reduced input/output coupling and adjustable high-side transmission zeroes
JPH09232805A (ja) 1996-02-21 1997-09-05 Nagano Japan Radio Co 高周波用ロ−パスフィルタ
US5689221A (en) * 1994-10-07 1997-11-18 Lk Products Oy Radio frequency filter comprising helix resonators
US5929721A (en) * 1996-08-06 1999-07-27 Motorola Inc. Ceramic filter with integrated harmonic response suppression using orthogonally oriented low-pass filter
US6255917B1 (en) * 1999-01-12 2001-07-03 Teledyne Technologies Incorporated Filter with stepped impedance resonators and method of making the filter

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6046568B2 (ja) * 1978-10-25 1985-10-16 株式会社日立製作所 Ｕｈｆチユ−ナの同調回路及びその共振周波数の調整方法
JPH0744364B2 (ja) * 1990-02-08 1995-05-15 富士電気化学株式会社 有極形低域通過フィルタ

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4179673A (en) 1977-02-14 1979-12-18 Murata Manufacturing Co., Ltd. Interdigital filter
US5124675A (en) * 1989-02-16 1992-06-23 Electric Industry Co., Ltd. LC-type dielectric filter
US5307036A (en) * 1989-06-09 1994-04-26 Lk-Products Oy Ceramic band-stop filter
US5379011A (en) * 1992-10-23 1995-01-03 Motorola, Inc. Surface mount ceramic filter duplexer having reduced input/output coupling and adjustable high-side transmission zeroes
US5689221A (en) * 1994-10-07 1997-11-18 Lk Products Oy Radio frequency filter comprising helix resonators
JPH09232805A (ja) 1996-02-21 1997-09-05 Nagano Japan Radio Co 高周波用ロ−パスフィルタ
US5929721A (en) * 1996-08-06 1999-07-27 Motorola Inc. Ceramic filter with integrated harmonic response suppression using orthogonally oriented low-pass filter
US6255917B1 (en) * 1999-01-12 2001-07-03 Teledyne Technologies Incorporated Filter with stepped impedance resonators and method of making the filter

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090153270A1 (en) * 2007-12-11 2009-06-18 Telegaertner Karl Gaertner Gmbh High-pass filter
US7952451B2 (en) * 2007-12-11 2011-05-31 Telegaertner Karl Gaertner Gmbh High-pass filter
CN102265456B (zh) * 2008-12-25 2014-12-24 日本电气株式会社 基于组合导通孔结构的滤波器
US8970327B2 (en) 2008-12-25 2015-03-03 Nec Corporation Filter based on a combined via structure
CN106463805A (zh) * 2014-03-24 2017-02-22 瑞典爱立信有限公司 同轴滤波器及其制造方法
US20170110776A1 (en) * 2014-03-24 2017-04-20 Telefonaktiebolaget Lm Ericsson (Publ) Coaxial filter and method for manufacturing the same
US10050322B2 (en) * 2014-03-24 2018-08-14 Telefonaktiebolaget Lm Ericsson (Publ) Coaxial filter and method for manufacturing the same

Also Published As

Publication number Publication date
US20020036552A1 (en) 2002-03-28
EP1191625A3 (en) 2003-05-14
FI115331B (fi) 2005-04-15
FI20002090A0 (fi) 2000-09-22
EP1191625A2 (en) 2002-03-27
FI20002090A (fi) 2002-03-23

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